This invention relates to a fluid tight rotary mechanical fluid coupling between a pair of relatively rotatable seal members in which the fluid sealing occurs between rotating axial mating faces, and more particularly to an arrangement wherein a non-rotating floating seal member is mounted in a housing separate from a rotating seal member and the axial sealing faces are biased into sealed engagement.
Fluid coupling apparatus that incorporates a rotating fluid seal between the axial mateable sealing faces of a pair of relatively rotatable parts thereof is known. Typical of such apparatus is rotary union of the kind used for effecting the transfer of fluid from a stationary fluid source to a fluid conduit in the form of a rotating spindle, shaft, clutch hub or other such device into which fluid is to be fed. Illustrative is "Rotating Union with Replaceable Sealing Assembly" shown in U.S. Pat. No. 4,817,995, issued Apr. 4, 1989 to Deubler et al. wherein a rotor seal member and a stator seal member are assembled in concentric relation in a common housing for relative rotation and passing fluid. The stator and rotor are axially biased towards one another such that the axial seal faces thereof are in engagement and define a rotating seal interface in the housing that is perpendicular to the axis of rotation. The rotor seal member is journalled on a bearing for rotation relative to the housing and includes a threaded shaft which extends from the housing to be affixed to the rotating spindle for rotation therewith.
Fluid conducting rotating unions give satisfactory service when operated at low or moderate speeds, such as about 2,000 rpm, but when operated at relatively high speeds, such as between 4,000 to 6,000 rpm and higher, encounter difficulties, typified by bearing failure, rapid wear, overheating, etc. Likewise, these rotating fluid unions give satisfactory service when conducting fluids at low or moderate pressures, but are oftentimes incapable of holding high pressures, or encounter operating difficulties under high pressures.
While the reasons for failure either at high speed, or high pressure, or combinations of both, are not completely understood, it is generally believed important that the respective rotor, stator, and spindle axes be maintained concentric with the axis of rotation during operation. Vibration and wobble can be produced if the spindle end is not accurately machined, or is damaged, or if the mass of the fluid union is not coaxial with the axis of the spindle.
However, the end face of the threaded rotor shaft and end face of the spindle (or mounting shoulder of the device mounted to) are typically very small, particularly in relationship to the mass and overall geometrical size of the complete fluid union housing which must be cantilevered at the end of the spindle, which can set up a mechanical disadvantage. When installing the union, the spindle end portion must be cleaned of chips and inspected for burrs or dents, such as would prevent accurate engagement between the axial end faces of the spindle and rotor.
Notwithstanding these precautions, at spindle speeds in the 2,500 rpm range and higher, harmonic vibrations can be induced if the mounting surfaces are not perfectly abutted and maintained in a plane perpendicular to the axis of rotation of the spindle to which fluid is to be supplied. These induced vibrations cause bearing failures in the fluid union itself. More seriously, these vibrations can lead to bearing failures in the spindle, or in the item to which the fluid union is mounted. Ultimately this can lead to quality problems and failures in the output operation of the spindle assembly.
The failures, as listed above, are also believed to result in part from the fluid supply hose being supported to the fluid union. The fluid supply hose is typically mounted to a fluid inlet at one end of the housing inlet, whereby to communicate fluid to the stator. Unless supported, this supply hose will place a load on the bearing.
Also, it is believed that tension forces placed on the fluid union in order to support the hose, which forces are countered only by bearings in the fluid union, will produce the same failures.
As is now appreciated, more pressure on the rotating seal interface to maintain axial contact between the sealing faces correlates into more friction, higher torque and thus more wear. A floating seal would be desirable to compensate for possible axial misalignment and wear.
At present, no one-piece fluid coupling unit is believed capable of meeting the demands and loads to which the marketplace is exposing these fluid couplings.
In accordance with this invention, a rotary fluid coupling for effecting the transfer of fluid from a stationary fluid source to a rotary member, such as a spindle, comprises a stationary housing assembly having an interior chamber, a stator assembly including a plunger non-rotatably mounted in the chamber, and a rotor assembly including a sleeve anchored to the spindle for rotation therewith, the rotor and stator assemblies each including a sealing member having a seal face facing axially. The sealing members are mounted, respectively, in the plunger and sleeve such that the sealing faces are engaging. Cooperating flats on the plunger and in the housing prevent the plunger from rotating relative to the chamber but allow the plunger axis to shift or be slightly inclined to the axis of rotation as a result of misalignment of the axis of the spindle end under rotation.
A biasing arrangement in the chamber acts against the plunger to maintain the sealing faces of the two members in abutted engagement to form a gapless rotary sealing interface. The housing assembly comprises an L-shaped bracket having an opening, and a cup-shaped member projecting axially from the bracket and forming therewith the interior chamber and positions the opening adjacent to the rotor. The forward end of the plunger which mounts the seal member thereof is positioned in the opening and is configured so a not to rotate relative to the housing but to permit minor movements of the plunger axis transversely to the spindle axis and as well as axially rearward from the opening along the axis.
The two-piece design wherein the rotor assembly is mounted to the spindle but mechanically separate from the stator assembly, advantageously eliminates the need of costly bearings to support the rotor assembly.
Advantageously, because of its two-piece construction, the fluid coupling herein is smaller, lighter, uses fewer parts, and uses no bearings.
Advantageously, mounting the stator plunger such that the sealing end face thereof "floats" relative to the housing axis and axis of rotation allows the sealing interface to maintain sealed engagement under high rotational speeds without placing forces and movements on bearings.
The rotor assembly herein advantageously mounts to the spindle to allow for a more liberal tolerance to the mounting specifications required of the spindle manufacturer.
The rotor and stator assembly herein advantageously allows the sealing interface to compensate for the spindle axis shifting from coincidence with the rotation axis.
These and other advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.